Hub to shaft connection

This Regular utility patent application claims the benefit to an earlier and Provisional patent application 60/797,772 filed on May 4, 2006 and entitled CENTRIFUGAL IMPELLER TO SHAFT MOUNTS.

1. Field of the Invention

The present invention relates to impellers mounted to a rotary shaft, and more specifically to a centrifugal impeller.

2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98

A centrifugal impeller mount on a rotary shaft of the prior art is shown in FIG. 1 . In this prior art arrangement, an interference fit is used to secure the impeller to the shaft by a tight fit. The shaft includes a smaller diameter portion 13 and a larger diameter portion 12 . The impeller 14 includes a central hole having a larger diameter portion and a smaller diameter portion that forms a tight interference fit with the shafts, the interference fits occurring at locations 16 and 18 on FIG. 1 . As the impeller spins, the fit loosens due to centrifugal forces. For heavily centrifugally loaded impellers, the fit has to be very large. This usually causes assembly and disassembly problems. Also, sometimes the impeller and shaft are of different materials and this too can cause problems with the fit. If the impeller has a higher coefficient of thermal expansion than does the shaft, at high temperatures the impeller will expand more than the shaft, and therefore the fit will loosen even more. When the centrifugal force from rotation is added, the fit will loosen even more. U.S. Pat. No. 6,481,970 B2 issued to Mukherjee et al on Nov. 19, 2002 and entitled COMPRESSOR WHEEL WITH PRESTRESSED HUB AND INTERFERENCE FIT INSERT is one prior art reference that shows this design.

It is therefore an object of the present invention to provide for an impeller mounted to a rotatable shaft with a fit that will not loosen during rotation.

It is another object of the present invention to provide for an impeller that can be mounted to the rotatable shaft without pre-stress such that the impeller can more easily be inserted onto the shaft.

The present invention is an inverted fit between the impeller and the shaft in order to use the centrifugal forces to promote a tight fit between the two. As the impeller spins faster, the fit tightens instead of loosening as in the prior art fit. The inverted fit of the present invention is also good for impellers and shafts that have different materials with different coefficients of thermal expansion.

FIG. 1 shows a prior art arrangement of a tight fit between an impeller and a rotary shaft.

FIG. 2 shows the present invention with the inventive inverted fit between the impeller and the shaft.

The present invention is shown in FIG. 2 in which an impeller 14 of a centrifugal pump or compressor is tightly fitted to a shaft 12 . The shaft includes a larger diameter portion 12 and a smaller diameter portion 13 . An inner annular groove 22 and an outer annular groove 20 is formed in the shaft, with axial extending portions 26 and 24 defined by the annular grooves 22 and 20 . this forms an inner axial extending portion 26 and an outer axial extending portion 24 on the shaft.

The impeller 14 includes an inner axial extending member 32 and an outer axial extending member 34 that define an annular groove 33 formed within the hub of the impeller. The axial extending members 32 and 34 of the impeller are sized and shaped to fit within the annular grooves 20 and 22 of the shaft. The fits are intended to be as tight as possible in order to provide a tight and secure fit between the impeller and the shaft, and to be loose enough to allow the impeller to be fitted onto the shaft during assembly or disassembly. An inwardly facing projection 35 of the impeller extends radially inward more than the section 36 in order to allow for the impeller to more easily slide onto the shaft. The inwardly extending projection 35 will form a tight fit against the shaft on which it abuts. The inward projection 35 is shown to be formed on the hub instead of the shaft because this method would be easier to manufacture than would placing a projection on the shaft. However, the projection could also be on the shaft instead of the hub.

As the impeller and shaft rotate together, the impeller will grow in the radial direction due to centrifugal forces acting thereon. The two axial extending members of the impeller will still abut against the axial extending portions 26 and 24 of the shaft to maintain a tight fit between the impeller and the shaft. Also, if the impeller is formed from a material that has a higher coefficient of thermal expansion than does the shaft, the inverted fit of the present invention will also maintain a tight fit under high temperatures.